This invention relates to a motionless mixer for combining liquid components and to a particular apparatus and method which are particularly effective for the purpose of mixing a low viscosity liquid into a stream of high viscosity liquid.
It has become common practice to use motionless mixers for mixing or dispersing one liquid component into another under both laminar and turbulent flow conditions, and a large body of apparatii has been developed for this purpose. Many have their origins in the concepts invented by Armeniades et al, described in U.S. Pat. No. 3,286,992 issued Nov. 22, 1966 in which a left-hand and right-hand twisted series of axially aligned elements are in a tube. Another in-line mixing concept has self-nesting, abutting and axially overlapping elements, as shown in the patent of King, U.S. Pat. No. 3,923,288 issued Dec. 2, 1975.
A particularly difficult problem for in-line multiple element mixers is that of mixing flowable materials which have widely differing viscosities, a problem which is commonly encountered in the manufacture and/or mixing of polymers. Under laminar flow conditions the low viscosity material tends to tunnel or "snake" its way through and around the mixing elements without blending sufficiently with the high viscosity material.
In the operation of any laminar flow mixer, one or more mixing mechanisms may play a role. These include laminar shear mixing, elongation or extensional mixing, distributive mixing, and molecular diffusion mixing. Prior mixing devices tend to favor or rely upon certain of these mechanisms, to the exclusion of the others. For example, the dual viscosity mixer shown in King, U.S. Pat. No. 4,808,007 issued Feb. 28, 1989 relies primarily upon molecular diffusion, by inserting into the main stream flow a thin layer or striation of the low viscosity liquid, and thereafter moving the combined streams through a conventional static mixer. A disadvantage of this technique resides primarily upon the release of molecular diffusion to the exclusion of the other mixing techniques. Also, such a system suffers the disadvantage of high back pressure induced by the necessity for forcing the mixture through an elongated conventional static mixer in order to provide a sufficient residence time for diffusion to become effective.